In a blast furnace, iron-oxide raw material such as iron ore is reduced with coke, for example, to produce molten pig iron. Generally, in operating a blast furnace, from viewpoints of safe operation and facility-related constraints, the temperature at a furnace top and the temperature near a tuyere of the blast furnace need to be controlled within a predetermined temperature range. Conventionally, from a viewpoint of resource conservation, for example, a technique of injecting pulverized coal into a blast furnace has been proposed to decrease the amount of coke used.
For example, Patent Literature 1, focusing on the combustion temperature in raceways of tuyere ends, proposes decreasing the coke ratio by charging metallic iron such as scrap iron or reduced iron into a blast furnace in the operation in which pulverized coal is injected at a constant rate. When molten pig iron is produced by using a blast furnace, the production amount of the molten pig iron per unit capacity of the blast furnace is required to be increased by sufficiently utilizing the capability of the blast furnace. As an index indicating such a production amount of molten pig iron, a productivity is used. Patent Literature 1 describes that a productivity of 2.19 to 2.40 t/(d·m) can be achieved.